1. Field of the Invention
The invention is in the field of heavy duty axle housings useful for large and heavy trucks in which a banjo housing is provided at or adjacent the center of the axle housing to accommodate the differential drive gears and laterally extending tubular members are formed in a rectangular cross-section to withstand torsional and vertical loading strains and stresses and to resist metal fatigue caused by pounding of the vehicle over rutted and potholed roads. The invention also lies in the field of manufacturing methods for axle housings using novel sheet steel material of uniform thickness.
2. Description of the Prior Art
As pointed out in the patent to Riemenschneider, U.S. Pat. No. 1,945,076, rear axle housings for motor vehicles have been manufactured by various methods all of which require careful selection of the starting stock material, special bending equipment and the employment of skilled operators. Generally, the prior methods contemplate stamping out blanks and shaping them by known bending methods into upper and lower halves of the axle housings which are welded together along longitudinal seams on each side to extend the full length of the housing. Such methods are expensive because a considerable percentage of the stock material is wasted due to the irregular outline of the blank and because of the excessive length of the weld.
The present methods which have been developed to overcome the problems noted in Riemenschneider are the hot forging methods such as those developed by Schneider et al, U.S. Pat. No. 2,674,783 which requires the use of expensive equipment dies and the services of skilled forging operators and welders, while at the same time requiring a blank having an irregular outline which is expensive because of the substantial waste of material.
Further, waste occurs not only in the material lost in cutting or stamping the blank but also takes place in forming the axle housing by hot forging and welding as for example in the Reimenschneider patent above-mentioned wherein a slotted tube is formed from strip stock, then heated and the end of the heated tub placed in a suitable female die to forcibly engage a complementary male die and thereby produce a predetermined upsetting of the blank which is enlarged by additional working to spread the upset. An additional step is required to outwardly weld a part thereof to form a frustoconical portion. That portion is then enlarged into an annular portion which is machined to a smooth finish and provides part of the housing for the axle. The added parts which are removed represent additional waste.
An additional example of a banjo-type drive axle housing having a very short tapered portion made by stamping of relatively thin sheet metal is found in U.S. Pat. No. 4,068,541 to Sakamoto et al. However, in the Sakamoto et al patent, the inner banjo shape adjacent the taper portion is reinforced by welding fixed partitions positioned to double the thickness in regions along the inside of the taper of the casing.
The present invention utilizes technology similar to the hot forming and bending technology of Schneider et al, U.S. Pat. No. 2,674,783 rather than stamping and internally reinforcing. The older efforts of stamping as well as the newer efforts of reinforcing a stamped banjo-shaped axle housing are to be distinguished from hot forming and bending operations which in accordance with the present invention are required to provide a faster fade in and adjacent to the transition zone between the differential receiving portion and the beam arms of the axle housing.